The present invention relates to apparatus for manipulating sheets which consist of flexible material, such as thin paper, plastic foil or the like. More particularly, the invention relates to improvements in apparatus for engaging and transporting discrete sheets of paper or the like downstream of a device which subdivides a running tape band, web or strip of flexible material into discrete panels or sheets. Still more particularly, the invention relates to improvements in apparatus of the type wherein an oncoming sheet enters an elongated path which is defined by two conveyor units forming part of a so-called catcher assembly.
It is already known to intercept and guide sheets of paper or the like immediately downstream of the station or locus where the sheets are formed, e.g., downstream of a cross cutter which normally includes drum-shaped rotary knife holders serving to sever a running strip, tape, band or web of paper or the like (hereinafter referred to as paper web or simply web) at predetermined (normally regular) intervals so that the web yields a succession of discrete sheets or panels which are transported to the next processing station, e.g., to a stacker where the sheets are piled up on top of each other preparatory to packaging, binding or another treatment. As a rule, the path for the running web is horizontal or substantially horizontal so that one of the rotary knife holders is located above and the other knife holder is disposed below the horizontal path. Cross cutters which can be utilized to subdivide a running paper web into a succession or file of discrete sheets are disclosed, for example, in U.S. Pat. Nos. 4,201,102 and 4,255,998 granted to Willy Rudszinat. For the sake of convenience, the disclosures of the patents to Rudszinat are incorporated herein by reference. During severing, the knives which are carried by and orbit about the axes of the respective rotary holders advance in the direction of transport and at the speed of movement of the running web. The leader of the freshly severed sheet or the leader of the web immediately downstream of the cutting plane is supposed to enter a predetermined path so as to ensure that each and every sheet will be transported in a predictable way and will reach the next processing station in a predetermined orientation as well as after elapse of a preselected interval of time following arrival of the preceding sheet. Such task cannot be performed by heretofore known sheet intercepting, guiding and transporting apparatus with a requisite degree of predictability and reproducibility. The reasons for unreliable operation of heretofore known sheet engaging and transporting apparatus are numerous and include the inability of such apparatus to adequately compensate for the tendency of sheets to flex or curl and/or for the tendency of currents of air which develop as a result of orbital movement of the knives to change the direction of movement of the sheets so that the leaders of the sheets often strike against rather than slide along the guide means downstream of the severing location, as well as insufficient versatility (especially the inability of conventional apparatus to conform their mode of operation to changes in flexibility, dimensions and/or consistency of the material of the web) and/or a combination of such factors. It has been found that the leader of the freshly severed sheet or the leader of the running web often exhibits a pronounced tendency to curl, not only because the severing device normally receives the web from a source of supply wherein the web is stored in the form of a roll (i.e., that the web exhibits a tendency to curl in the same direction in which it was wound on the core of a reel or the like) but also due to gravity since the path for discrete sheets or downstream of the severing location is normally horizontal or substantially horizontal. The center of curvature of the leader of the web and/or of the leaders of successive sheets is located below the selected path for the sheets, and the length of the radius of curvature of the curling leading end of the web or the leading end of each discrete sheet depends on the tendency of the web to curl as well as on the flexibility of the material of the web and the weight or mass of the flexible stock per unit of length.
The just discussed tendency of the freshly formed sheets to leave their desired path presents many problems, especially in high-speed paper processing machines, because the quality of the ultimate product (e.g., a wrapped and packed ream of stacked paper sheets or a stack of ruled paper sheets which are assembled into a steno pad, exercise book or the like) depends to a considerable degree on the accuracy with which the sheets are guided in the region immediately downstream of the severing location.